Please take a look here:
1) You can use this with Windows (incl. MinGW) as well as Linux. Alternative you can only use the code as an example.
2) Step-by-step tutorial how to use serial ports on windows
3) You can use this literally on MinGW
Here's some very, very simple code (without any error handling or settings):
#include <windows.h>
/* ... */
// Open serial port
HANDLE serialHandle;
serialHandle = CreateFile("\\\\.\\COM1", GENERIC_READ | GENERIC_WRITE, 0, 0, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0);
// Do some basic settings
DCB serialParams = { 0 };
serialParams.DCBlength = sizeof(serialParams);
GetCommState(serialHandle, &serialParams);
serialParams.BaudRate = baudrate;
serialParams.ByteSize = byteSize;
serialParams.StopBits = stopBits;
serialParams.Parity = parity;
SetCommState(serialHandle, &serialParams);
// Set timeouts
COMMTIMEOUTS timeout = { 0 };
timeout.ReadIntervalTimeout = 50;
timeout.ReadTotalTimeoutConstant = 50;
timeout.ReadTotalTimeoutMultiplier = 50;
timeout.WriteTotalTimeoutConstant = 50;
timeout.WriteTotalTimeoutMultiplier = 10;
SetCommTimeouts(serialHandle, &timeout);
Now you can use WriteFile() / ReadFile() to write / read bytes.
Don't forget to close your connection:
CloseHandle(serialHandle);